Hyperdiffusive dynamics in conjugated polymer blends and fullerene absorbing solutionsстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:We have observed the hyperdiffusive dynamics of light scatterers accompanied by their ballistic motion by a dynamic light scattering (DLS) technique in blends of semiconducting polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], MEH-PPV) with a low-molecular-weight organic acceptor 2,4,7-trinitrofluorenone, TNF) and in fullerene C-60 solution. The DLS autocorrelation function has been found to follow the Kohlrausch-Williams-Watt function with the exponent beta in the range of 0.5-2, depending on the laser power, scattering vector, optical absorption and type of sample. We show that the hyperdiffusive dynamics (beta > 1) results from laser-induced convection caused by optical absorption at the DLS probing wavelength. The convection appears in the DLS data as a ballistic motion with velocities in the range of 5-60 mu m s(-1) depending on the laser power, type of sample and their absorption. The convection is driven by the local temperature difference, Delta T similar to 0.1-0.2 K, as evaluated from thermal lens effect measurements. We demonstrate that by decreasing the absorbed laser power, laser-induced hyperdiffusion can be avoided in both the polymer and fullerene samples so that the inherent thermal molecular motion can be probed. Specifically, in the polymer solutions, we have found a slow relaxation mode with the characteristic spatial spectrum of the inverse relaxation time T-s alpha q(4). This mode has been assigned to the coupled motion of entangled conjugated polymer chains.